1. Field of the Invention
The present invention relates to an apparatus for controlling a reciprocating movement or operating stroke of a reciprocating member, such as a reciprocating spindle quill of a tapping or similar machine tool.
2. Discussion of the Prior Art
The control apparatus used for such a reciprocating member is usually adapted to detect and control the reciprocating movement of the reciprocating member, according to a signal generated by a relatively simple encoder. In a tapping machine, for example, the spindle quill is operatively connected to a spindle drive motor, so that the quill is fed in the forward tapping direction and retracted in the reverse direction, in synchronization with the forward and reverse operations of the drive motor. The operating stroke of the spindle quill is controlled by counting the number of pulses generated by the encoder after the spindle drive motor is started to operate in the forward direction. When the count of a counter used for counting the encoder pulses reaches a predetermined value, the operating direction of the motor is reversed, to retract the spindle quill from the lower end of the stroke to the home position of the machine, i.e., the upper end of the stroke.
The encoder is one of the important components of the control apparatus, and is conventionally incorporated within the spindle head of the machine and protected by a suitable covering member. The encoder is mounted on an encoder substrate, on which light-emitting diodes LED) are provided to permit the use to inspect the pulse signals produced by the encoder. When the visual inspection of the pulse signals is effected, the covering member must be removed to obtain an access to the light-emitting diodes.
In the conventional arrangement of the encoder and the inspection diodes, the maintenance or adjustment of the encoder which requires the removal of the covering member is cumbersome and time-consuming. The machine may fail to normally operate in connection of the reciprocating movement of the spindle quill, due to a defective or abnormal condition of the encoder. In particular, the encoder may fail to normally function, since the photoelectric detector of the encoder is exposed to oil and dust. Accordingly, the encoder should be inspected at suitable maintenance intervals, for assuring reliable operation of the machine.